If the earpiece/ ear speaker of your iPhone 6s Plus stops working or produces sounds on lower levels you should check some of the factors that might be the reason behind it. Which are:

• Check if your ringer switch is on
• Check if your volume levels are in an optimum range
• Check if you have a noise-canceling feature on in iPhone turned on. Try turning it off and see if it returns your phone to normal audio levels.
• Check the settings at Settings > Accessibility > Audio/Visual > Phone Noise Cancellation.
• Sometimes the speaker may have debris or dirt in it. Causing it to cease properly functioning properly. Cleaning it may also resolve the issue.

If none of the procedures resolve the issue regarding your ear speaker issue you may need to get it looked at it by professionals. Here at ifixit bd, we have experienced repairmen who specialize in repairing and resolving issues regarding your iPhone 6s Plus. We have service points located in Dhaka, Bangladesh.